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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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194                               ALASKAN GLACIEE STUDIES
Application to Former Greater Expansion of Glaciers. In Yakutat Bay itself there has been a comparatively recent advance of the glaciers, during which Nunatak and Hidden Glaciers pushed forward until they united and extended their combined glacier front far up Russell Fiord.1 The Russell Fiord Glacier was then between 15 and 20 miles farther down the fiord than the front of Nunatak Glacier has been at any time since its discovery, and between 10 and 15 miles farther than Hidden Glacier front. The expansion of Turner and Hubbard Glaciers may have been less notable, but still great, a branch of the expanded Hubbard-Variegated Glacier perhaps joining the Russell Fiord Glacier. The evidence of this advance is a series of stratified glacial gravels overridden by the ice and thereby sculptured by glacial erosion and veneered by a deposit of unassorted till, bowlders, and other glacial debris, while at the head of Russell Fiord is an abandoned lake beach, formed by the waters held in behind the ice dam. That the period of ice advance was brief is proved by the fact that its erosion did not succeed in removing the gravels accumulated before the advance. Until 1906-07 Hidden Glacier was still receding from its advanced position, and recession was still in progress in Nunatak Glacier till 1909-10. The evidence that the recession had been rapid, and that the period even of maximum expansion was recent is complete, for on the outer part of the area reached by the glacier, and on and below the level of the lake beach, the forest has not yet reached the mature stage, while between this and the glacier the vegetation diminishes in age and stage of development, and for a distance of several miles from the glacier fronts only annual and perennial plants and individual young alder and willow bushes are growing. Similar conditions occur in front of Hubbard Glacier in Russell Fiord and Disenchantment Bay.
It is noteworthy that this advance followed a period during which the glacier fronts had been farther back than now, and which was of such long duration that mature forests grew on the shores of the fiord over which the advancing glaciers swept, and even up the valleys where ice now stands, as is conclusively shown by fragments of wood now being carried out by the glaciers from regions at present not forested.
Northeast of Yakutat Bay, on the other side of the St. Elias Range, are the Deza-deash and Kaskawulsh valleys, within which McConnell2 found convincing evidence in 1904 of former, long, narrow lakes which he believes to have been dammed by the expanded glaciers of the upper Alsek region, that is by ice tongues connected with the through-glacier systems that reach Yakutat Bay. The preservation of driftwood and the lack of mature forest upon the abandoned lower beaches of these lakes, which were 150 feet deep, and the legends of the natives suggest that the advance took place less than a hundred years ago, probably indicating a glacial expansion here contemporaneous with the last maximum of the Yakutat Bay region. The youth of the trees growing on these lower beaches, the spruces not being over 8 inches in diameter, proves how recently t.Tn'a advance took place.
Brooks recognized the beach terraces in 1899 as of lacustrine origin,8 but thought the lake had been drained by canyon-cutting below. The discovery of better-developed,
i Tarr, R. S. and Martin, Lawrence, Bull. Amer. Geog. Soc., Vol. XXXVlil, 1908, pp. 161-166; Tarr, R. S., Professional Paper 64, U. 8. Geol. Survey, 1909, pp. 125-137.
»McConnelJ, R. G., The Huane Mining District, Geol. Survey of Canada, Ann. Rept., Vol. XVI, 1904, pp. 2A-4A.
* Brooks, A. H., Reconnaissance from Pyramid Harbor to Eagle City, Alaska, 21st Ann, Rept., U. S. Geol. Survey, Port II, 1901, p. 849.